This invention relates to a belt conveyor device for the suspended transport in particular, by means of vacuum, of goods to be conveyed, particularly plate-like workpieces, metal sheets or the like, comprising at least one conveyor belt which can be moved along a holding track and comprising a vacuum device which holds the goods to be conveyed, by suction, against a transport side of the at least one conveyor belt.
Vacuum belt conveyors of this type are frequently used in the sheet metal processing industry, in areas where metal sheets or workpieces made of sheet metal, such as can lids, panels in the automobile industry or the like, have to be conveyed suspended from one processing station to a further processing location. Vacuum belt conveyors are used in particular for the transport of non-ferromagnetic materials, for example for aluminum sheets, plastics sheets or wooden materials. The transported goods to be conveyed are held by suction, by the vacuum device, against the conveyor belt or conveyor belts, and are thereby held on the conveyor device whilst they are conveyed by means of the circulating conveyor belts.
Known vacuum belt conveyor devices generally necessitate special vacuum conveyor belts, which comprise holes disposed at a spacing from each other through which air is sucked into a vacuum channel disposed on the underside of the conveyor. Specially formed suction pockets are normally constructed around the holes on the belt itself. The vacuum which secures the metal sheet or the like to the conveyor is generated in these suction pockets when the workpiece is placed thereon.
Therefore, in known vacuum belt conveyor devices air is generally sucked through the conveyor belt and the vacuum which is necessary for holding the components to be conveyed is available directly on the transport side of the conveyor belt itself. For this purpose, the conveyor belts are of special construction, and are provided, for example, with individual flexible suction devices which protrude from the transport side and which surround the suction openings, or with vacuum pockets which are open towards the transport side, so as to be able to hold the metal sheets on the belt. Due to their special form of construction, conveyor belts for vacuum belt conveyor devices are very expensive. Moreover, they are also subject to a high degree of wear, because the individual suction devices which protrude from a belt are frequently damaged or torn off completely, and then have to be laboriously repaired or replaced. Vacuum pockets which are let into the belt itself are in fact less susceptible to wear than are protruding individual suction devices. In vacuum conveyor belts such as these, however, the seal between the belt and component to be conveyed is often unsatisfactory, so that unusually powerful vacuum devices have to be used in order to hold the components to be conveyed securely on the conveyor.
The object of the present invention is to create a belt conveyor device of the type cited at the outset, the at least one conveyor belt of which is only subjected to a very low degree of wear, and with which it is possible to use inexpensive standard belts for the transport of the goods to be conveyed, such as those which are otherwise used only on magnetic belt conveyors on which ferromagnetic components are held against the transport side of the belt by means of a magnetic field which acts through the belt.
This object is achieved according to the invention by providing the vacuum device with a multiplicity of suction nozzles, which are disposed on the holding track, at the side of and next to the at least one conveyor belt, so that their nozzle edges which point towards the transported goods to be conveyed are situated at a short distance from the latter or from the transport side of the conveyor belt.
The invention therefore constitutes a departure from the well-worn path of making the vacuum which is necessary for holding the components to be conveyed available on the conveyor belt itself, in suction devices or vacuum chambers which are disposed thereon and which circulate with the belt. According to the invention, the vacuum which is necessary for holding the components is now generated at fixed locations next to the conveyor belt or conveyor belts, by means of many suction nozzles, which are disposed in series, which are aligned towards the transported goods to be conveyed, and which hold the latter by suction against the conveyor belt or conveyor belts which run at the side of and as close as possible to the suction nozzles. Since there is only a short distance between the front nozzle edges of the suction nozzles and the transport side of the conveyor belt, or between the front nozzle edges and the flat face of the transported component which is held by suction, and in the ideal case, for example, this distance amounts only to a few tens of millimeters, the amount of secondary air which is sucked through this gap which remains between the nozzle edge and the component is also insignificantly small as soon as the suction nozzle concerned is completely covered by the transported component. Therefore, even though the transported components do not come into direct contact with the suction nozzles, they are secured by the latter and are pulled against the conveyor belt, by means of which they are transported from a transfer station to a delivery station.
Since according to the invention the air which is necessary for holding the components is no longer sucked through the belt itself, but local, invariable vacuum zones, through which a component passes in succession on its transport path, are instead created on the conveyor device by the multiplicity of fixed suction nozzles, simple standard belts can be used as conveyor belts, the transport side of which forms a simple flat surface without additional suction devices, vacuum indentations or the like having to be provided. For example, it is possible to use belts for the conveyor device such as those which were hitherto used only on purely magnetic belt conveyors.
The suction nozzles are preferably disposed between two parallel conveyor belts which can be moved along the holding track. They then form a central suction region between the two conveyor belts for the metal sheets or the like, which in their suction-held state are supported uniformly on the two conveyor belts. It is also possible for the vacuum device to comprises at least two groups, which each have a plurality of suction nozzles and which are disposed in series next to the longitudinal edges of the belt on both sides of the conveyor belt or conveyor belts. In this embodiment, suction regions for the components to be conveyed are therefore situated at both longitudinal edges of the conveyor belt or conveyor belts.
It is particularly advantageous if a separate vacuum generator is associated with each suction nozzle, so that the air which is sucked in by a suction nozzle, in the suction region of which there is no workpiece, has no effect on the effective suction capacity of the suction nozzles, the suction regions of which are transporting a workpiece. The vacuum generators for the individual suction nozzles may consist of fans, venturi nozzles or of what are termed xe2x80x9cair moversxe2x80x9d, which are also termed xe2x80x9cair quantity boostersxe2x80x9d and which, similarly to venturi nozzles, can suck in large amounts of ambient air at one end with the aid of compressed air.
The vacuum generators for at least one part of the suction nozzles are preferably connectable and disconnectable individually and/or in groups. It is thereby possible deliberately to interrupt the generation of the vacuum at selected suction nozzles and thus to release the transported components exactly at a desired location by turning off the vacuum for a short time.
The vacuum generators are advantageously disposed in the vicinity of the nozzle edges of the suction nozzles, which results in a particularly compact form of construction and whereby losses due to suction lines which are too long can be avoided. The suction nozzles can be disposed at a constant, fixed spacing from each other on the holding track of the belt conveyor device. It is particularly advantageous, however, if the suction nozzles are disposed on the holding track so that their spacing from each other is adjustable, especially if the number of suction nozzles which are provided on the holding track of the conveyor is variable. The spacings of the suction nozzles and the number thereof can then be adjusted in the optimum manner, depending on the size and weight of the components to be conveyed, so that for each component to be conveyed a sufficient number of nozzles always simultaneously generates the vacuum at the upper surface thereof and thereby hold the component, but so that no more suction nozzles have to be used than are necessary. It is also possible, of course, to achieve a corresponding effect with an arrangement of the suction nozzles at a fixed spacing from each other, for example if the components to be conveyed are particularly light, by arranging for only each second or even for only each third nozzle to be effective and to generate suction at the upper surface of the goods to be conveyed, with the remaining nozzles only being effective during the transport of heavier components.
A particularly advantageous embodiment of the invention is created if magnet units which act on the transport track are associated with the conveyor belt or conveyor belts, so that by means of the magnet units the belt conveyor device, as a combination conveyor, can transport ferromagnetic components which are pulled against the conveyor belts by magnetic fields which act through the latter, whilst non-ferromagnetic components are held against the belts by suction by means of the vacuum device. At least one part of the magnet units is advantageously connectable and disconnectable individually or in groups, as is known in the art, so as to be able to release the ferromagnetic sheets or the like at the desired location.
If the conveyor belt or conveyor belts are reinforced with steel inserts, not only do they have a particularly long service life, but the belts themselvesxe2x80x94provided that the conveyor is provided with magnet unitsxe2x80x94are pulled strongly by the magnets against the underside of the conveyor and are seated against the latter in a substantially air-tight manner, so that in this region also the vacuum device cannot suck in secondary air. The conveyor belt or conveyor belts are advantageously pressed against the holding track by means of retaining strips which act on their longitudinal sides, in order reliably to prevent sagging of the belts if the latter are not provided with steel inserts and/or if the conveyors are not provided with magnet units.
The suction nozzles preferably have an approximately circular or elliptical cross-section in the region of their nozzle edges, but can also be rectangular, particularly for nozzles which directly adjoin each other on the conveyor, so that practically no free space, in the region of which no suction can be generated, remains between two adjacent nozzles in the longitudinal direction of the conveyor.
The conveyor belt or conveyor belts can be disposed circulating around a box-like supporting construction on the underside of which the holding track is formed, wherein the magnet units and/or the vacuum generator are disposed in the interior of the supporting construction. This results in a particularly compact, low-maintenance form of construction. It is also possible, of course, for the vacuum generators to be disposed outside the supporting construction.
Other features and advantages of the invention follow from the description given below and from the drawings, in which a preferred embodiment of the invention is explained in greater detail by way of example.